The present invention relates to a valve mechanism for a double overhead camshaft (DOHC) engine with horizontally opposed cylinders, and more particularly to a lubricating system for valve mechanism. In accordance with requirement for increase of the power of the engine, the horizontally opposed cylinder engine with a DOHC type valve mechanism having a hydraulic valve-lash adjuster has been proposed. The valve mechanism comprises a cam, a rocker arm, and a hydraulic valve-lash adjuster, a hydraulic system for the hydraulic valve-lash adjuster, and a lubricating system for lubricating respective sliding portions. In particular, it is desirable to effectively circulate oil of the lubricating system including oil of the hydraulic system.
Japanese Utility Model Application Laid-Open No. 61-17408 discloses a lubricating system for a single overhead camshaft (OHC) engine in which oil is independently supplied to an oil gallery for a hydraulic valve-lash adjuster and a passage provided in a camshaft in the axial direction thereof. Surfaces of cams and journals of the camshaft are lubricated by oil through the passage in the camshaft.
If the system in the prior art is used for the valve mechanism for the double overhead camshaft (DOHC) engine, a large amount of oil must be used for the hydraulic valve-lash adjusters. Consequently, the amount of oil for lubrication become short.
In a horizontally opposed cylinder engine, it is necessary to keep pressure of oil constant for the valve-lash adjusters. Since spring load per valve reduces with reduction of the diameter of the valve, it is necessary to control the pressure of oil so as to prevent the valve from being pushed up by the valve-lash adjuster. Because the number of the camshafts in the DOHC engine increases, torque for driving the camshafts increases, so that tensile strength of a belt for the camshafts is increased. The increase of the tensile strength may occur seizure of the journals of the camshafts. Further, since the hydraulic valve-lash adjusters are upwardly or downwardly inclined with respect to the horizontal, oil is liable to leak during the stop of the engine.